1. Field of the Invention
This invention relates to a new process for the production of new polyisocyanate preparations containing urea and/or biuret groups by the reaction of organic polyisocyanates with subequivalent quantities of organic compounds containing isocyanate-reactive groups, of which at least some are primary or secondary amino groups; to the polyisocyanate preparations obtainable by this process; and to their use in the production of plastics by the isocyanate polyaddition process, more especially in the production of molded plastics by reaction injection molding.
2. Description of the Prior Art
The production of urethane-modified polyisocyanate preparations, i.e. isocyanate-terminated prepolymers and semiprepolymers, especially those based on polyisocyanates or polyisocyanate mixtures of the diphenylmethane series (4,4'-diisocyanatodiphenylmethane, mixtures thereof with 2,4'- and, optionally 2,2'-diisocyanatodiphenylmethane or phosgenation products of aniline/formaldehyde condensates which, in addition to these diisocyanates, contain higher homologues thereof) and various polyhydroxyl compounds is known (cf. for example EP-A Nos. 10,850 or 66,130: DE-OS Nos. 2,347,207, 2,404,166, 2,513,793, 2,513,796, 2,620,222, 2,622,104, 2,732,182, 2,737,338, 2,804,375, 2,810,596, 2,815,579 or 2,913,126: U.S. Pat. Nos. 3,644,457, 4,055,548, 4,234,714 or 4,321,333 and also GB-P No. 1,369,334).
The processes described in these prior publications generally comprise liquefying diisocyanatodiphenylmethane, more especially 4,4'-diisocyanatodiphenylmethane, which is solid at room temperature or reducing the tendency towards crystallization during storage at low temperatures of polyisocyanate mixtures of the diphenylmethane series which are liquid at room temperature.
However, in the prepolymerization or semiprepolymerization of polyisocyanates with polyols, certain compromises have to be made in terms of the structure and molecular weight of those polyols in order to achieve a liquefying effect, so that polyhydroxyl compounds which produce the best mechanical properties in the polyurethane plastics produced from the polyisocyanate preparations often cannot be used for the prepolymerization or semiprepolymerization. Another disadvantage is that the urethane groups present in the prepolymers or semiprepolymers show poor thermal stability compared with urea or amide groups, so that the plastics predominantly containing urethane groups which are produced from the prepolymers or semiprepolymers generally show poorer mechanical properties at elevated temperatures than comparable plastics in which the urethane groups or at least some of the urethane groups are replaced by urea groups.
The production of polyisocyanate preparations containing urea and/or biuret groups is also known. Thus, DE-PS No. 1,215,365 describes the production of relatively high molecular weight biuret polyisocyanates by reaction of at least 3 moles of an organic diisocyanate with 1 mole of a .omega.,.omega.'-diaminopolyether having an average molecular weight of 200 to 6000, to which a small quantity of a corresponding .omega.,.omega.'-dihydroxy or of a .omega.-hydroxy-.omega.'-aminopolyether may optionally be added. GB-P No. 1,078,390 describes the production of liquid polyisocyanate compositions by heating an organic diisocyanate with a solution of an aromatic diamine in an organic solvent for 1 to 4 hours to a temperature of 150.degree. to 200.degree. C.
Isocyanate compositions containing urethane groups in addition to biuret and urea groups may also be obtained by reaction of mixtures of ketones and dior poly-amines with di- or poly-isocyanates in accordance with GB-P No. 1,263,609. According to DE-OS No. 1,963,190, liquid, diprimary aromatic diamines, of which the reactivity to isocyanates is reduced by electrophilic or sterically hindering substituents, are reacted with polyisocyanates to form liquid, stable biuret polyisocyanates. According to DE-OS No. 2,010,887, mono- and/or polyamines containing secondary amino groups are reacted with polyisocyanates at 80.degree. to 200.degree. C. to produce liquid biuret polyisocyanates. According to DE-OS No. 2,032,547, urea-modified isocyanates which are liquid at -20 to +80.degree. C. are formed from these starting components. DE-OS No. 2,261,065 describes the reaction of organic polyisocyanates with subequivalent quantities of aliphatic or cycloaliphatic diamines to form the corresponding biuret polyisocyanates. According to DE-OS No. 3,003,543, urea-modified polyisocyanates are obtained by reaction of simple polyisocyanates with subequivalent quantities of polyamines containing more than three non-aromatically bound amino groups. According to DE-OS No. 3,114,638, special diisocyanates and/or diamines containing aromatically bound isocyanate and amino groups are used for the production of aromatic urea- and/or biuret-modified polyisocyanates.
However, the products obtained in accordance with these prior publications have never acquired any significance, especially for the production of semirigid, optionally foamed, elastomeric molded plastics of the type obtainable by reaction injection molding. The reason for this lies primarily in the fact that the diamines hitherto used for producing the polyisocyanate preparations do not correspond to the diamines or polyamines which have hitherto been successfully used as reactants for organic polyisocyanates in the production of high-quality molded plastics by reaction injection molding.
Accordingly, the object of the present invention is to provide a process for the production of polyisocyanate preparations containing urea and/or biuret groups which combines the following advantages:
1. The reactants used for the starting polyisocyanates, optionally in addition to other compounds containing isocyanate-reactive groups, are diamines and/or polyamines of the type corresponding to those diamines and/or polyamines which have hitherto been processed with organic polyisocyanates by the one-shot process to form particularly highquality polyisocyanate polyadducts. The reactants in question are, in particular, the relatively high molecular weight "aminopolyethers" described in detail hereinafter and, above all, the low molecular weight aromatic diamines containing amino groups sterically hindered by alkyl substituents which are described in detail hereinafter. Previously, these low molecular weight diamines in particular have had to be used in admixture with the other reactants for the polyisocyanates, i.e. the diamines have been used as chain-extending agents (cf. for example GB-P No. 1,534,258). Also, it has previously not been possible to incorporate these diamines, which are responsible for the favorable mechanical properties of the polyisocyanate polyadducts into the polyadducts by way of the polyisocyanate component. PA1 2. The production of the polyisocyanate preparations, especially when using the particularly preferred starting polyisocyanates (polyisocyanate mixtures of the diphenylmethane series containing a considerable amount of 4,4'-diisocyanatodiphenylmethane), leads to a reduction of the tendency towards crystallization of the starting polyisocyanates at room temperature or, when using 4,4'-diisocyanatodiphenylmethane, leads to the liquification of this starting diisocyanate. PA1 3. The process may readily be carried out at relatively low temperatures and, in addition, has a wide range of variation, i.e. it is also possible to react low molecular weight di- and/or polyamines other than the preferred aromatic diamines just mentioned, which previously have given difficulty soluble ureas or polyureas when reacted with organic polyisocyanates, with organic polyisocyanates to form liquid, storable polyisocyanate preparations. PA1 (A) organic polyisocyanates having an NCO-content of about 10 to 50% by weight or mixtures of organic polyisocyanates having an NCO-content of about 10 to 50% by weight with PA1 (B) organic compounds containing isocyanate-reactive groups, maintaining an equivalent ratio of isocyanate groups in component (A) to isocyanatereactive groups in component (B) of about 2:1 to 100:1, characterized in that component (B) contains mixtures of PA1 (a) organic compounds having an (average) molecular weight of 500 to about 20,000 and containing at least two isocyanate-reactive groups and PA1 (b) organic compounds having a molecular weight of 60 to 499 and containing at least two isocyanatereactive groups wherein the equivalent ratio of (a) to (b), based on the isocyanate-reactive groups, is about 100:1 to 0.1:1, component (a) being based on polyethers or polyesters with a molecular weight of 500 to about 20,000 which have a functionality of at least two in the context of the isocyanate addition reaction and which contain alcoholic hydroxyl groups attached to primary and/or secondary carbon atoms and/or aromatic and/or (cyclo)aliphatically bound, primary and/or secondary amino groups or of mixtures of such compounds and component (b) being selected from PA1 (b1) aromatic diamines or triamines containing primary or secondary amino groups and having a molecular weight of 108 to 499, PA1 (b2) (cyclo)aliphatic diamines and/or triamines containing primary and/or secondary amino groups and having a molecular weight of 60 to 499, PA1 (b3) organic compounds with a molecular weight of 61 to 499 which have a functionality of at least two in the context of the isocyanate addition reaction and which contain both (i) at least one aromatically and/or (cyclo)aliphatically bound primary and/or secondary amino group and also (ii) at least one alcoholic hydroxyl group attached to a primary or secondary carbon atom, PA1 (b4) at least dihydric alcohols optionally containing ether or ester groups and having a molecular weight of 60 to 499 and PA1 (b5) mixtures of compounds (b1) to (b4), with the proviso that at least 25% of the isocyanatereactive groups present in components (a) and (b) are primary or secondary amino groups.
This object is achieved by the process described in detail hereinafter in which mixtures of certain relatively high molecular weight compounds containing isocyanate-reactive groups, especially amino groups, with certain low molecular weight compounds containing isocyanate-reactive groups, especially amino groups, are reacted with excess quantities of organic polyisocyanates to form storable polyisocyanate preparations containing urea and/or biuret groups. The fact that the process according to the invention is workable is surprising insofar as it was known that most of the low molecular weight diamines used in the process according to the invention, on account of their high reactivity to isocyanate groups, react instantaneously with organic polyisocyanates to form difficulty soluble ureas or polyureas.